This invention relates to the design of an arm for the carriage of a read/write head for motion in juxtaposition to a magnetic recording surface for the recording of digital data.
It is known to control such arms by servo loops in which the read/write head is used to detect position information from dedicated portions of the magnetic recording surface, typically a disk, and to use this information in controlling the motor which moves the read/write head with respect to the disk so as to access various portions of its surface, in addition to the read/write head's primary function of reading and writing actual digital data to areas of the disk. As is typically the case in servo controlled systems, it is possible that mechanical resonance can be encountered in operation of the mechanical parts of this system. In order to avoid allowing the mechanical resonance to be excited by the operation of the servo circuit, it has been the typical prior art practice to design the mechanical portions of the apparatus which are subject to resonance and the servo circuit such that the resonant frequency of the mechanical system is outside the bandwidth of the servo system. Typical methods of designing the arm to control its resonance frequency involve making it either heavier or out of a more expensive, stiffer material, so that resonance is reduced, or its frequency is moved out of the servo circuit's bandwidth. However, these solutions are not optimum; for example, it may well be that the preferred mechanical design of the apparatus is such that its natural resonant frequency is near the sampling rate. Any departures from the desired design, therefore, would involve a compromise in performance.